### Instruction:
Give me a working Python function for binary_search.
### Answer:
```python
def binary_search(items, target):
    low = 0
    high = len(items) - 1
    while low <= high:
        mid = (low + high) // 2
        value = items[mid]
        if value == target:
            return mid
        if value < target:
            low = mid + 1
        else:
            high = mid - 1
    return -1
```

### Instruction: